Problem with slow feed moves stuffering on my 3DR Delta

Hi, this is my very first post here on this forum.
I'm completely new to the 3D printing hobby, this is my first build and I'm
just getting started to learn the configuration basics of the printer firmware (Repetier).
However I'm a good programmer, I've build some CNC machines and I'm confident with
electronics etc. Now I think I definitely need some expert advice.

I've recently got my 3DR Delta printer up and running (motion parts, no extruder
yet etc), and started to try out the configuration and some travel / feed moves
by sending gcode in manual mode (from repetier host).
The printer uses GT2 belts and pulleys instead of the fishing line otherwise is
pretty much a straight up build from RichRap instructions.
The printed parts are in ABS, printed with a Zortrax M200 (at work).

The printer moves ok (smoothly) when doing travelling moves at high speed
(F7000+), but for slower moves (F100-1000) i noticed that the moves are VERY stuttering.
This is for a simple single command, so there's no Slicer involved or anything. If I send:
G1 F100 X60
The carriage litterally shakes it's way to the target destination!
Otherwise dimensions and coordinates seems to be right, end-stops are working
etc, so I think I got the basic configuration right.

Is this behavior normal, are deltas not supposed to be smooth when travelling
slow? or what am I doing wrong?
I don't think that I have problems with the electronic setup, e.g. steppers seem
to run smooth when controlling them with custom code, so I'm leaning towards
that something is up with my configuration.

I've tried adjusting many of the parameters but with no visible change to the
problematic stuttering behavior.
The params that caught my interest a little more than others was the below ones:

DELTA_SEGMENTS_PER_SECOND_PRINT 200 // Tried from 40-600
DELTA_SEGMENTS_PER_SECOND_MOVE 100

Also:
MAX_DELTA_SEGMENTS_PER_LINE 22 // tried up to 30
MAX_FEEDRATE_X 380 // haven't played around with this yet.

Acceleration is 1000-2000 and jerk 20

My setup:
---------
RUMBA board
Repetier firmware 0.92
drv8825 stepper drivers, adjusted for 1.4A (tried with 16 & 32 microsteps, same
results).
SureStep 2A stepper motors (NEMA 17)
24V power supply

If helpful, I could post a video on youtube of the problem...

I too am totally new with 3D printers and have finished a build on my Delta as well.

It's weird but when I home my machine at a F7000 it sounds fine, but only when I tell it to move down to let's say 10mm above the build plate at the same F7000 it does the stuttering too,
I can home it again and it sounds fine, also when I actually print something it sound fine there too, not sure why I hear the stuttering or hesitation only when move down toward ZERO.

Good luck on your calibration, it was a pain, I'm still tweaking it, and waiting on a new extruder setup, my current one is not doing to good, I have to run the prints very slow.

Did you ever come up with a solution? I'm also notice vibration at low speeds, I think it is related to the microstepping not being fine enough or just cheap drivers.

gitsly,

Stuttering is a very common problem when using 8-bit controllers with Delta printers.

Here are some of the reasons:
- Delta math is more complex, and it's doing floating point on an 8-bit processor, and some movements cause more calculations than others. The more DELTA_SEGMENTS_PER_SECOND used the worse it will be, use at lower end of these settings. If you search on the forum you will find what setting others have used (I don't recall).
- Some people try to use graphics controllers - these should never used with a Delta that is using an 8-bit controller, not near enough processing power. You could use one like this.
- Since you are commissioning, make sure the current on the drivers is not too high. If they are overheating then they do a short duration thermal shutdown, this could be for the briefest fraction of a second.
- Too many microsteps. I'd recommend not using more than 16 microsteps with this board, I think you have it at 32, that's double the load.
- Rule of thumb when printing: do so from an SD card. (I know you are testing manually via USB.)

Repetier is supposed to be a bit faster than Marlin, so it's good you have that.

Some people have acceptable results. You should be able to download someone's Repetier config file, or ask them to post it here. It's been a while but I checked it over:

I notice that your Z axis steps per mm is not the same as X and Y. Not sure if it matters, but you should make them the same.
I notice you are not using quadstepping. You may want to turn that on. It's a trick they use to get more steps out since the mhz is not near high enough!

I started with a Rumba in my big delta because at that time I could not find a 32-bit controller known to work on one. I tried Marlin first, then Repetier.
Symptoms I would have were shuddering/stuttering on rapids, and blobs in outside perimeters caused by brief stuttering. A stutter can be enough to cause missed steps if it happens at the wrong time, causing shifted layers and a ruined print. I replaced my Rumba with a Smoothie and never looked back (shudders).

I really hope you get it to work.

---

My printer: Raptosaur - Large Format Delta - [www.paulwanamaker.wordpress.com]
Can you answer questions about Calibration, Printing issues, Mechanics? Write it up and improve the Wiki!

@gitsly

do you have a video of the problem.. I have been using a 3dr since 1 year and i have had no stuttering as you say. i am using delta segments as 100. check you acceleration and jerk

Thanks for all the input, however I've resolved the issue since a while ago (actually since then, I've built a Kossel style delta as well ).
I boiled down the problem to be related to by DRV stepper drivers,
During troubleshooting I used the stepper drivers from my CNC machine (DQ540MA or somehting) which generated really smooth (no noise or stuttering) movement, so I figured that it must have been the stepper drivers.
I was able to solder the DECAY pin to 5V (according to this page: [www.morgan3dp.com]) activating FAST decay mode.
Then the stuttering movement went away! Still not as smooth as the CNC driver thingys, but for the cost and size of these things, I find it quite ok. And the printer works amazingly well!

I hope we see decay hacked DRV8825 ready_to_buy soon.
It is a PITA to solder these tiny legs without burning the chip.
-Olaf

You can also try this workaround to make the drv's to behave.